Toughening and strengthening of advanced ceramics with rare earth additives

doi:10.1016/j.ceramint.2005.03.021

Ceramics International

Volume 32, Issue 4, 2006, Pages 423-429

https://doi.org/10.1016/j.ceramint.2005.03.021 Get rights and content

Abstract

Al₂O₃/(W,Ti)C composite ceramic materials reinforced by rare earth additives have been fabricated by the hot pressing technique. Microstructure, flexural strength, toughening and strengthening mechanisms are analyzed. The maximum flexural strength and fracture toughness of the yttrium reinforced Al₂O₃/(W,Ti)C ceramic are 853 MPa and 6.1 MPam^1/2, respectively, which are approximately 20% and 16% higher than for the corresponding material without yttrium. Acting mechanisms of the yttrium additive are mainly the purification of interface, the subsequent increase in the interface bonding strength and strengthening by nanometer sized particles. Because of the co-existence of both strong and weak interfaces, synergistic interactions of toughening mechanisms like crack bridging, crack branching, crack defection and microcracking, etc. are enhanced. Therefore, fracture toughness of the rare earth reinforced Al₂O₃/(W,Ti)C ceramic material is increased. The developed new ceramic materials are found to achieve higher fracture resistance when used as cutting tools.

Introduction

At present, Al₂O₃-based ceramic material is one of the most widely used ceramics in practice. However, the intrinsic brittleness still exists as a fatal weakness for ceramic materials. In order to reduce the brittleness and to increase the strength and toughness, a great deal of research work has been done [1], [2], [3]. Mechanical properties of alumina-based ceramics have been improved by the incorporation of one or more reinforcing phases such as TiC, TiN, TiB₂, SiC particulates, SiC whiskers, B₄C, ZrO₂, WC, (W,Ti)C, Ti(C,N), Cr₃C₂, NbC, etc. Investigations on toughening mechanisms such as crack deflection, crack branching, crack bridging, microcracking, transformation, toughening by residual thermal stress and their synergistic interactions, etc. are still active [1], [4], [5], [6], [7], [8].

Rare earth elements, working as a series of effective additives, have got widespread applications in current research of advanced ceramic materials [9], [10]. They can be used not only as the stabilizer of the tetragonal zirconium oxide but as the sintering aid for Al₂O₃, TiB₂, TiC, SiC, Si₃N₄, sialon and AlN ceramics [9], [10], [11], [12]. As a result, physical and mechanical properties of these ceramics have been noticeably enhanced. However, other possible acting mechanisms of rare earth elements have rarely been reported elsewhere. In the present study, Al₂O₃/(W,Ti)C ceramic composites reinforced by rare earth additives are fabricated. Microstructure, mechanical property, toughening and strengthening mechanisms and cutting performance are investigated in detail.

Section snippets

Experimental procedures

Commercially available high purity alumina and (W,Ti)C powders were used as the starting materials with average sizes of 0.8 μm and 1.0 μm, respectively. The raw materials were blended with each other (with 35 wt.% (W,Ti)C) and doped with different amounts up to 2 wt.% of pure rare earth metal additive such as yttrium (Y). The doping process and the following ball-milling process have been performed under a N₂ protective atmosphere. The mixtures were subsequently homogenized with absolute alcohol

Mechanical property

The maximum flexural strength of Al₂O₃/(W,Ti)C ceramics is about 853 MPa when 0.25 wt.% Y is added (Fig. 1), which is about 20% higher than that of the corresponding material without yttrium. Then, with the increase of yttrium content, the flexural strength decreases slowly.

Under the experimental conditions, the incorporation of yttrium can improve the fracture toughness of Al₂O₃/(W,Ti)C ceramic materials when its content is less than 1.5 wt.% (Fig. 2). Particularly, when 0.5 wt.% Y is added the

Conclusions

The addition of rare earth additives such as yttrium of a suitable amount in a proper way can notably improve the flexural strength and fracture toughness and fracture resistance of Al₂O₃/(W,Ti)C ceramic material.

Acknowledgements

The Foundation for University Key Teacher by the Ministry of Education, China (Grant No. 2058), the Research Fund for the Excellent Young & Middle-aged Scientists, Shandong Province (Grant No. 2000-49) and the Natural Science Fund, Shandong Province (Grant No. Y2001F02), are all greatly appreciated for supporting this project.

References (17)

Y. Fu et al.
SiC whisker toughened Al₂O₃–(Ti W)C ceramic matrix composites
Scripta Mater.
(2001)
J. Gong et al.
The influence of TiC-particle-size on the fracture toughness of Al₂O₃–30 wt. TiC composites
J. Eur. Ceram. Soc.
(2001)
W. Acchar et al.
Effect of Y₂O₃ addition on the densification and mechanical properties of alumina-niobium carbide composites
Ceram. Int.
(2001)
Z.S. Rak et al.
Manufacture and properties of Al₂O₃–TiN particulate composites
J. Eur. Ceram. Soc.
(1998)
J. Rödel
Interaction between crack deflection and crack bridging
J. Eur. Ceram. Soc.
(1992)
A.G. Evans
Perspective on the development of high toughness ceramics
J. Am. Ceram. Soc.
(1990)
X. Ai et al.
Development and perspective of advanced ceramic cutting tool material.
Key Eng. Mater.
(1995)
P.F. Becher
Microstructural design of toughened ceramics
J. Am. Ceram. Soc.
(1991)

There are more references available in the full text version of this article.

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Toughening and strengthening of advanced ceramics with rare earth additives

Abstract

Introduction

Section snippets

Experimental procedures

Mechanical property

Conclusions

Acknowledgements

Scripta Mater.

J. Eur. Ceram. Soc.

Ceram. Int.

J. Eur. Ceram. Soc.

J. Eur. Ceram. Soc.

Perspective on the development of high toughness ceramics

J. Am. Ceram. Soc.

Development and perspective of advanced ceramic cutting tool material.

Key Eng. Mater.

Microstructural design of toughened ceramics

J. Am. Ceram. Soc.